Tuberculosis (TB) is a disease caused by the bacteria Mycobacterium tuberculosis. It most commonly affects the lungs, although it can affect other parts of the body. Medications are available to treat TB and must be taken as prescribed by your provider. Depending on the medication(s) prescribed, the duration can be from four months to nine months or more.

Worldwide, TB remains a leading cause of death. In the United States, TB is on the decline; the number of cases reported in 2012 is the lowest since the 1950s.

TB can be fatal if not recognized and treated. However, TB is treatable and preventable. Identifying and treating those who are infected, but who have not yet become ill with active TB, can prevent the spread of TB in the community.

HOW DOES TUBERCULOSIS OCCUR?

The tuberculosis (TB) bacteria are spread through the air from a person who is ill with active TB that involves the lungs or airways. The bacteria are contained in small, airborne droplets created by coughing or sneezing. Anyone who inhales these droplets is called a "contact." A contact can be someone you spend a lot of time with, such as a family member, friend, or co-worker.

The contact person does not usually develop active TB immediately. In some cases, the person's immune system is able to remove the bacteria and he/she does not develop the disease.

In other cases, the person develops an immune response that controls the bacteria by "walling it off" inside the body. This causes the bacteria to become dormant or asleep. The person does not develop active TB or become ill at this time, but is said to have latent TB infection (LTBI). Up to one-third of the world's population is infected with LTBI.

Latent TB — During this latent stage of TB, also called TB infection, the person is well and cannot spread the infection to others. If the person is treated at this stage, active TB can usually be prevented. Treatment is recommended for individuals who are at increased risk for the development of active TB. (See 'Treatment of latent tuberculosis' below.)

Active TB — Active TB may develop if latent infection is not fully treated. This is called reactivation TB, and it occurs in 5 to 10 percent of people with latent infection.

Reactivation TB may occur if the individual's immune system becomes weakened and is no longer able to contain the dormant bacteria. The bacteria then become active and make the person sick with TB. This is called TB disease.

The greatest risk for developing reactivation TB disease is within the first two years following the initial infection. Reactivation can also occur in people with HIV, diabetes mellitus, malnutrition, or those who take medications that weaken the immune system, such as steroids or cancer chemotherapy. It can also occur with aging and weakening of the immune system. Reactivation may also occur for other, unknown reasons.

HOW IS LATENT TUBERCULOSIS DIAGNOSED?

Latent tuberculosis (LTBI) can be diagnosed with a skin test or with a blood test.

TB skin tests are performed by injecting a small amount of a solution just beneath the surface of the skin, usually on the forearm. The solution contains an inactivated portion of the TB bacteria. Most individuals previously infected with TB develop a skin reaction (a red or swollen bump) at this site.

Reasons for skin testing — Tuberculin skin tests are performed for persons who are at risk of having LTBI:

●If the person is a healthcare or laboratory worker who may be a new employee to a healthcare facility or have contact with patients infected with TB.

●If the person knows he or she was exposed to someone with active TB. If the first test is negative, a second test usually will be performed 8 to 10 weeks later.

●If the person requires a medication that may weaken the immune system, such as steroids or some rheumatologic medications.

●If the person has HIV infection.

Interpreting the results — The skin test should be examined 48 to 72 hours after the solution is injected under the skin. The skin is examined to determine if there is swelling (the size of the bump). The area may also be reddened, but redness should not be measured.

A trained healthcare provider (not the patient or a family member) interprets the test as positive or negative based on the size of the bump and criteria for what size of reaction is considered positive in certain patient groups. Anyone who has a bump larger than 15 mm is considered to have a positive test, and some people with a bump that is 5 mm (eg, HIV) or 10 mm (eg, recent immigrant from a region with a high rate of TB) are considered to have a positive test if they are at higher risk for developing TB.

What does a positive TB skin test mean? — The TB skin test indicates that TB bacteria are in the body. It cannot determine if a person has active TB disease or LTBI. Further testing is needed to determine if the person has active or LTBI. People who have active TB usually have symptoms, such as a cough (usually persisting for several weeks), fevers, night sweats, and/or unexplained weight loss. (See 'Further testing' below.)

Skin testing after a positive test in the past — Anyone who has had a positive reaction to the TB skin test in the past will usually have a positive reaction in the future. Even after taking medication to treat TB, the reaction to the skin test will remain positive. Therefore, anyone who has a positive skin test does not need to have skin testing again. Repeat testing can rarely cause a large and painful skin reaction at the injection site.

BCG vaccine — A TB vaccine called Bacillus Calmette-Guerin (BCG) is given in many countries to prevent infection with TB. It usually is given to infants, although it may be given again at other times. BCG offers protection against TB in children, but typically does not offer continuing protection. BCG is not routinely used to prevent TB in the United States.

This vaccine may or may not cause a positive skin test. In the United States, a positive reaction to a TB skin test is interpreted as positive, regardless of prior BCG vaccination. Previous BCG vaccination should NOT stop a person from obtaining a TB skin test unless the person had a positive reaction in the past. (See 'Skin testing after a positive test in the past' above.)

Two-step skin testing — In some people, the TB skin test is falsely negative because the immune system's response to TB has weakened over time. This may occur in people who were exposed to TB many years before. If a first skin test is negative, a second skin test may be done one to two weeks later. Performing the first test may "boost" the immune system, allowing it to react if the person was previously exposed to TB.

If the person has two negative tests, this is considered a true negative. If the second test is positive, further testing will be done to determine if the person has active or LTBI. (See 'Further testing' below.)

Two-step testing establishes a baseline in people who will need skin testing at regular intervals in the future (eg, healthcare workers, employees and residents of institutions, such as prisons or nursing homes).

Blood tests for TB — Blood tests known as interferon gamma release assays (IGRAs) are now available in most areas to test for TB infection. The blood test may be offered instead of, or in addition to, the skin test. Blood tests may simplify TB testing because they do not require the person to make a return trip to read the test reaction. In addition, blood test results for LTBI are not affected by prior immunization with BCG vaccine or by prior infection with harmless bacteria from the environment.

Further testing — If the TB skin test or blood test is positive, a healthcare provider will ask some specific questions, perform a physical examination, and obtain a chest x-ray to determine if person has active TB, either currently or in the past. In some cases, the person will be referred to a TB specialist for this evaluation.

If these tests indicate that the person has active TB, rather than LTBI, the treatment regimen is different than that of someone with LTBI. (See 'Active tuberculosis' below.)

TREATMENT OF LATENT TUBERCULOSIS

Latent tuberculosis infection (LTBI) is treated with a medication or medications to kill the dormant bacteria. Treating LTBI greatly reduces the risk of the infection progressing to active tuberculosis (TB) later in life (ie, it is given to prevent reactivation). (See "Treatment of latent tuberculosis infection in HIV-negative adults".)

While undergoing treatment for TB (either infection or disease), it is important to avoid drinking alcohol and taking acetaminophen (Tylenol®). Both of these substances can make the liver work harder, potentially increasing the risk of liver injury from the medications.

Isoniazid — One of the most commonly used treatments for LTBI is isoniazid (INH). Isoniazid is a pill that is taken once per day for nine months. It is important to take the medicine every day and to finish the entire course of treatment since missing days or discontinuing the medicine early may not prevent active TB.

Rifampin — Another treatment option is a medication called rifampin. Rifampin is taken as two capsules every day for four months. Rifampin interacts with many other medications, such as hormonal birth control methods (skin patch, pills, vaginal ring), blood thinners, certain medications for high blood pressure, and many others. Therefore, it is important to discuss possible drug interactions with a healthcare provider.

Rifapentine — A rifampin-like medication, rifapentine, may be prescribed along with INH in some situations. It usually is taken once a week with the INH under direct observation by a trained healthcare worker. Its toxicities and drug interaction properties are similar to those of rifampin.

Monitoring during treatment — People who are being treated for TB should be monitored by a healthcare provider at least once per month to monitor for any signs of medication toxicity, such as liver injury. Signs of liver injury may include: unexplained tiredness, loss of appetite, nausea, vomiting, dark-colored urine, jaundice (yellowing of the skin or the white portion of the eye), fatigue, abdominal pain, or rarely, unexplained bruises. Anyone who experiences one or more of these problems should stop their medication immediately and notify their healthcare provider.

In certain special cases, monthly monitoring may also include blood tests to monitor the function of the liver or blood counts.

ACTIVE TUBERCULOSIS

Active tuberculosis (TB) disease occurs when the TB bacteria become “active” and cause a person to become ill. This usually occurs in the lung, although TB can affect any part of the body, including the lymph nodes, brain, kidneys, or bones. (See "Treatment of pulmonary tuberculosis in HIV-negative patients".)

If there is evidence on a chest x-ray or other signs that active pulmonary (lungs) TB is present, sputum cultures will be performed to culture (grow) the bacteria in the laboratory. This usually involves coughing up a "deep" specimen of phlegm from the chest. The phlegm is then sent to a laboratory and cultured to determine if TB bacteria are present. Other tests, such as a bronchoscopy or biopsy, may also be needed. A tissue biopsy may be performed to obtain specimens for culture if TB is suspected in other organs (such as lymph nodes or kidney). (See "Patient information: Flexible bronchoscopy (Beyond the Basics)".)

While waiting for the results of the culture (some results are positive within a day or two, but it may take as long as two months for the bacteria to grow in the laboratory), treatment with several (usually four) TB drugs is usually recommended. It is important to use more than one medicine and to take the medicines exactly as prescribed to reduce the risk of the bacteria becoming resistant to one (or more) of the medicines.

Tuberculosis (TB) is a disease that can easily be spread by anyone with active disease. As a result, United States laws require that anyone with active TB must be reported to the health department. Health department staff will work with the patient's healthcare provider and the patient to make sure that a safe and effective treatment regimen is completed.

Directly observed therapy (DOT) is a program used by public health departments to ensure that a patient safely takes his or her medication exactly as prescribed. With this program, a health worker watches a person swallow the TB medication every day. DOT may help to improve cure rates. (See "Adherence to tuberculosis treatment".)

The health department can also help to identify people who have been in contact with a person with active TB. Contacts are advised to have TB testing and treatment, if necessary.

Public health programs for TB are essential for several reasons:

●To reduce the number of new cases of TB (by identifying and treating people with LTBI in order to prevent disease from developing)

●To limit spread of the disease in the community (by monitoring and assuring safe, complete treatment of people with active TB).

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.